Bis-cycloheptyl-fused bis(imino)pyridine-cobalt catalysts for PE wax formation: positive effects of fluoride substitution on catalytic performance and thermal stability.

The α,α'-bis(imino)-2,3:5,6-bis(pentamethylene)pyridyl-cobalt(ii) chlorides, [2,3:5,6-{C4H8C(N(2-R1-4-R3-6-R2C6H2))}2C5HN] CoCl2 (R1 = Me, R2 = R3 = CH(p-FPh)2 Co1; R1 = Et, R2 = R3 = CH(p-FPh)2 Co2; R1 = i-Pr, R2 = R3 = CH(p-FPh)2 Co3; R1 = Cl, R2 = R3 = CH(p-FPh)2 Co4; R1 = F, R2 = R3 = CH(p-FPh)2 Co5; R1 = F, R2 = R3 = CHPh2 Co5'', R1 = R2 = Me, R3 = CH(p-FPh)2 Co6; R1 = R3 = Me, R2 = CH(p-FPh)2 Co7), have been synthesized by a one-pot template reaction of α,α'-dioxo-2,3:5,6-bis(pentamethylene)pyridine, cobalt(ii) chloride and the respective aniline in n-butanol. By contrast, the mixed cobalt(ii) chloride/acetate complex, [2,3:5,6-{C4H8C(N(2-F-4,6-(CH(p-FPh)2)2C6H2))}2C5HN]CoCl(OAc) (Co5'), was isolated when the corresponding template reaction was carried out in acetic acid. Structural characterization of Co4, Co5 and Co5'' revealed distorted square pyramidal geometries while six-coordinate Co5', incorporating a chelating acetate ligand, exhibited a distorted octahedral geometry. On activation with either MAO or MMAO, 2-fluoride-4,6-bis{di(p-fluorophenyl)methyl}-substituted Co5 showed maximum catalytic activity for ethylene polymerization at a high operating temperature of 60 °C (up to 2.1 × 107 g (PE) mol-1 (Co) h-1), producing highly linear (Tms > 121 °C), low molecular weight polyethylene waxes (Mw range: 1.5-5.0 kg mol-1) with narrow dispersity (Mw/Mn range: 1.7-2.9). End-group analysis of the waxes reveals β-H elimination as the dominant chain transfer process.